/*
 * Copyright 2002-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.context;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * 启动Spring的root WebApplicationContext的引导Servlet，简单对{@link ContextLoader}的代理。<br/>
 * Bootstrap listener to start up Spring's root {@link WebApplicationContext}.
 * Simply delegates to {@link ContextLoader}.
 * 
 * <p>
 * This listener should be registered after
 * {@link org.springframework.web.util.Log4jConfigListener} in
 * <code>web.xml</code>, if the latter is used.
 * 
 * <p>
 * For Servlet 2.2 containers and Servlet 2.3 ones that do not initalize
 * listeners before servlets, use {@link ContextLoaderServlet}. See the latter's
 * Javadoc for details.
 * <p>
 * 对于Servlet 2.2容器和Servle2.3这些没有在servlets之前初始化listers的，使用ContextLoaderServlet
 * 
 * @author Juergen Hoeller
 * @since 17.02.2003
 * @see ContextLoaderServlet
 * @see org.springframework.web.util.Log4jConfigListener
 */
public class ContextLoaderListener implements ServletContextListener {

	private ContextLoader contextLoader;

	/**
	 * Initialize the root web application context.
	 */

	public void contextInitialized(ServletContextEvent event) {
		this.contextLoader = createContextLoader();
		this.contextLoader.initWebApplicationContext(event.getServletContext());
	}

	/**
	 * Create the ContextLoader to use. Can be overridden in subclasses.
	 * 
	 * @return the new ContextLoader
	 */
	protected ContextLoader createContextLoader() {
		return new ContextLoader();
	}

	/**
	 * Return the ContextLoader used by this listener.
	 * 
	 * @return the current ContextLoader
	 */
	public ContextLoader getContextLoader() {
		return this.contextLoader;
	}

	/**
	 * Close the root web application context.
	 */
	public void contextDestroyed(ServletContextEvent event) {
		if (this.contextLoader != null) {
			this.contextLoader.closeWebApplicationContext(event
					.getServletContext());
		}
	}

}
